The present invention relates to a position detection device, and it especially relates to the position detection device that is used to locate the starting point of a circular, back and forth movement of the grating plate in the illumination case.
A Chinese Patent No. ZL00227988.6 discloses an illumination case that mainly includes a grating plate, an illumination filmstrip that contains multiple striped pictures, a transparent back plate, and a set of two step motors. The illumination filmstrip overlays the transparent back plate and is fixed against it. The grating plate spreads out and nestles up to the illumination filmstrip by means of stretch springs. The grating plate moves up and down in a circular fashion, and it is driven by the two step motors. With the movement of the illumination filmstrip relative to the grating plate, different striped pictures on the illumination filmstrip are displayed one by one, which causes a sensation to one viewing the pictures that the pictures are changing or moving. Because all of the striped pictures are displayed by means of the back-and-forth movement of the grating plate, in order to show the pictures clearly, the grating plate requires an accurate starting point of the circular movement and an accurate motion distance. This illumination case uses, as the benchmark, a mechanical position switch which the step motor touches when the motor changes its direction and moves downward. Many factors cause the grating plate to deviate from the benchmark during its movement, such as the nonlinear deviation in the motor""s movement and the thermal deformation of the illumination filmstrip, the grating plate and the transparent back plate. Although the control circuit of the step motors contains a timing regulation feature, the action sensitivity of the mechanical position switch is low, with a certain progressive error of the contacts causing low control precision. As a result, oftentimes elements of another picture appear in the displayed picture, resulting in a double-imaging in the displayed picture that reduces the clarity of the picture.
There is a need to provide a position detection device that accurately controls the starting point of the grating plate in its circular, up-and-down movement.
To realize the above object, the position detection device for illumination case of the present invention includes an illumination filmstrip, a grating plate, a transparent back plate, a set of two step motors for driving the grating plate to move up and down, and a one-chip microcomputer. The illumination filmstrip overlays the transparent back plate and is fixed against it. The grating plate spreads out and nestles up to the illumination filmstrip by means of stretch springs, and it links with the two step motors. The position detection device for illumination case of the present invention also includes two sensors and related sensing elements. These two sensors are fixed on the left side and the right side of the transparent back plate, respectively. The sensing elements are correspondingly fitted on the grating plate to set the starting point of the circular up-and-down movement of the grating plate. The current fixed position of the sensing element on the grating plate is taken as the benchmark, and the sensor now detects a reference signal. Once the starting point of the grating plate shifts, the benchmark also shifts accordingly, and the sensor detects a deviation signal, which is transmitted to the one-chip microcomputer for processing. By regulating the step motor on the same side of the grating plate, the starting point of the grating plate is led back to the preset location.
On the fixed position of each of the sensors and each of the sensing elements described in the present invention, a magnetic piece is correspondingly fitted to attract each other, to prevent the sensing elements and the sensors from separating far from each other, which would result in detection error.
The sensors described in the present invention can be infrared photoelectric sensors, supersonic sensors, or magnetic sensors; correspondingly, the sensing elements can be light reflecting chips, sound reflecting chips, or magnetic inductive chips.
In another embodiment of the present invention, an external display circuit is connected to the one-chip microcomputer, which includes a drive module for a seven-segment digital LED and three seven-segment digital LEDs. Instructions are input through the external buttons, and the one-chip microcomputer sets and controls the remaining time, the moving speed, and the moving step-distance of the grating plate. The actual data are displayed on the seven-segment LEDs. The one-chip microcomputer can output at least two synchronous control signals for controlling the synchronous operation of two or more grating plates of the illumination case.
Because of the use of the sensors, the detection of the benchmark of the grating plate is carried out after each moving circle. The detected data are processed by the one-chip microcomputer and are used to regulate the step motor to ensure the accurate positioning of the benchmark. Instructions can be input through the external buttons, and the one-chip microcomputer accordingly sets and controls the grating plate for its remaining time, moving speed, and moving step-distance, so that the grating plate keeps an accurate starting point of the circular movement and accurate moving distance. As a result, the double-imaging is eliminated on the displayed picture.